The current method of assessing the (anti-)androgenic potential of a compound in vivo is through the use of the Hershberger assay. This involves first castrating adult male rats, allowing the sexual accessory tissues to regress and then exposing the rats to the compound of interest in the presence or absence of an androgen. The OECD is currently validating this assay as part of their initiative to develop and validate in vitro and in vivo assays for the detection of endocrine disrupters. A drawback of this assay is that it requires the castration of the animals prior to testing and, not only is this procedure technically demanding but it is also not in-keeping with the 3Rs ethos (replace, reduce and refine) of animal welfare.
An alternative approach was recently proposed by Ashby and Lefevre (2000; Reg. Tox. Pharm., 31: 92-105) in which non-castrated weanling male rats are used instead of castrated adult male rodents. The objective of this research, therefore, is to evaluate the feasibility of using this assay an alternative to the classic Hershberger assay. To this end a series of studies will be performed, which will mimic those previously performed during the OECD validation of the Hershberger assay. Thus, two dose response studies will be initially performed using the anti-androgens, linuron and DDE. Two additional studies will then be performed using coded compounds, which will be supplied by the central repository at TNO (Holland). In all studies, male weanling rats, aged 21-22 days of age, will be exposed daily to the androgen, testosterone propionate, and to the compound of interest for 10 days. Flutamide will act as the anti-androgen positive control. Animals will be sacrificed 24h after the last exposures and necrospied. The following tissues will be excised from each animal, trimmed free of fat and weighed: liver, kidneys (paired), adrenal glands (paired), testes (separate), epididymides (separate), ventral prostate, seminal vesicles (with coagulating glands), levator ani and bulbocavernosus muscles and Cowper’s glands. Terminal body weights will also be taken. The conduct of all studies, as well as the conditions of test for each study, will be identical to those used in this laboratory for the Hershberger validation project. In addition, the coded weanling studies will use the same compounds as those used in the Hershberger assay. Finally, all data will be reported and analysed in the same way as those for the Hershberger assay. In this way, a direct comparison between the two assays can consequently be performed.
Tinwell et al (2007). Evaluation of the Antiandrogenic Effects of Flutamide, DDE, and Linuron in the Weanling Rat Assay Using Organ Weight, Histopathological, and Proteomic Approaches. Toxicological Sciences 100 (1), 54-65.